1. Field of the Invention
The present invention relates generally to an electric vehicle, and more particularly to a method for controlling the battery charging of an electric vehicle, in which if a battery is determined as a failure according to a conventional first failure criteria in a charging mode, the battery is inspected according to a second failure criteria less strict than the conventional first failure criteria and the battery charging is performed according to the result of the inspection.
2. Description of the Prior Art
Current automobile engines utilize energy obtained by burning fossil fuel in cylinders as their power, so exhaust gas generated in the cylinders includes harmful substances such as NOx, HC, CO, etc. These substances pollute the atmosphere and do harm to human beings, resulting in an environmental pollution problem.
Recently, electric vehicles that can resolve the aforementioned pollution problem have been developed and used. Such an electric vehicle includes a battery, a controller, a motor, a driving gear, etc. The electric vehicle is operated in such a way that the motor is driven by power from the charged battery and the driving gear is operated by power from the motor.
In such a case, in the battery of the electric vehicle, a plurality of cells constitute a battery module (12V), and a plurality of such battery modules constitute a battery pack so as to meet the required voltage of a driving source.
FIG. 1 is a flowchart showing a method for controlling the battery charging of a conventional electric vehicle. First of all, the voltage of the battery pack comprised of a plurality of battery modules is detected at a step S1. Subsequently, the average voltage (Vb_avg) of battery modules is calculated by dividing the voltage of the battery pack by the number of the battery modules constituting the battery pack at a step S2. Thereafter, a variable xe2x80x98ixe2x80x99 is set for xe2x80x980xe2x80x99 at a step S3, where the variable xe2x80x98ixe2x80x99 designates a battery module number.
Subsequently, a difference value (Vb_module(i)xc2x7Vb_avg) between the voltage (Vb_module(i)) of the battery modules and the average voltage (Vb_avg) is compared to a predetermined reference difference value (Vdiff_cut) at a step S4. If the difference value (Vb_module (i)xc2x7Vb_avg) is equal to or greater than the reference difference value (Vdiff_cut), a step S10 is performed; while if the difference value (Vb_module (i)xc2x7Vb_avg) is equal to or less than the reference difference value (Vdiff_cut), a step S5 is performed.
The voltage (Vb_module (i)) of the battery modules is respectively compared to a preset maximum failure reference voltage value (Vb_max) and a preset minimum failure reference voltage value (Vb_min) at the step S5. If the voltage (Vb_module (i)) of battery modules is equal to or greater than the maximum failure reference voltage value (Vb_max), or equal to or less than the minimum failure reference voltage value (Vb_in), the step S10 is performed; while if the voltage (Vb_module (i)) of battery modules is less than the maximum failure reference voltage value (Vb_max) and greater than the minimum failure reference voltage value (Vb_Min), a step S6 is performed.
The voltage (Vb_module (i)) of the battery modules is respectively compared to a preset maximum warning reference voltage value (Vb_warn_max) and a preset minimum warning reference voltage value (Vb_warn_min) at the step S6. If the voltage (Vb_module (i)) of the battery modules is equal to or greater than the maximum warning reference voltage value (Vb_warn_max), or equal to or less than the minimum warning reference voltage value (Vb_warn_min), a step S7 is performed; while if the voltage (Vb_module (i)) of the battery modules is less than the maximum warning reference voltage value (Vb_warn_max) and greater than the minimum warning reference voltage value (Vb_warn_min), a step S8 is performed.
Battery warning is set at the step S7. In this case, if the number of the warned battery modules is greater than a certain number (for example, three), the control process of the battery failure is performed.
Subsequently, a variable xe2x80x98ixe2x80x99 is increased by adding xe2x80x9c1xe2x80x9d to the variable xe2x80x98ixe2x80x99 at the step S8. It is determined whether the value of the variable xe2x80x98ixe2x80x99 is greater than the value obtained by subtracting 1 from the number of the battery modules at a step S9. If the value of the variable xe2x80x98ixe2x80x99 is greater than the value obtained by subtracting xe2x80x981xe2x80x99 from the number of the battery modules, the procedure returns to a main routine for controlling the entire state of the electric vehicle; while if the value of the variable xe2x80x98ixe2x80x99 is equal to or smaller than the value obtained by subtracting xe2x80x981xe2x80x99 from the number of the battery modules, the procedure returns to the step S4.
That is, the steps S3, S8 and S9 are provided for sequentially performing the steps S4 to S7 in regard to all the battery modules constituting the battery pack.
Battery failure is set at the step S10, and, in this case, both driving and charging are impossible.
However, in the above-mentioned conventional battery charging method for an electric vehicle, when only one battery module fails, both driving and charging are impossible. At this time, if the battery is left for a certain period of time without repair, there occurs a problem that even normal battery modules except for the failed battery module are deteriorated due to deep discharging caused by self-discharging.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method for controlling the battery charging of an electric vehicle, in which if a battery is determined as a failure according to a conventional first failure criteria in a charging mode, the battery is inspected according to a second failure criteria less strict than the conventional first failure criteria and the battery charging is performed according to the result of the inspection, so the battery can be charged when a part of battery modules fail, thereby preventing the performance of normal battery modules from being deteriorated due to deep discharging by self-discharging.
In order to accomplish the above object, the present invention provides a method for controlling the battery charging of an electric vehicle, comprising the steps of: determining whether the voltage of battery modules satisfies second failure criteria less strict than first failure criteria, if the voltage of the battery modules satisfies the first failure criteria in a charging mode; considering the state of a battery as a battery failure and not charging the battery, if the voltage of the battery modules satisfies the second failure criteria; charging the battery for a certain period of time on the charging condition of a failure mode stricter than the charging condition of a normal mode, if the voltage of the battery modules does not satisfy the second failure criteria; determining whether the voltage of the battery modules measured after the performance of the failure mode charging satisfies the first failure criteria; considering the state of a battery as a failure and not charging the battery, if the voltage of the battery modules measured after the performance of the failure mode charging satisfies the first failure criteria; and charging the battery on the charging condition of the normal mode, if the voltage of the battery modules measured after the performance of the failure mode charging does not satisfy the first failure criteria.